The present invention relates to a mounting method for mounting, for example, electronic components on a board, and more particularly to a mounting method which reduces the occurrence of defects during high density mounting of micro components.
The sizes of electronic components such as semiconductors are continuing to shrink and their mounting density onto a board is rising. For example, a mounting pattern for mounting micro components of about 0.6 mmxc3x970.3 mm in size at a 0.1 mm pitch on a board has already been commercialized. An extremely high degree of accuracy in mounting position is required for mounting components at a high density on a board with this type of narrow-pitch mounting pattern. Accordingly, more accurate placement of components as well as more accurate positioning of electrodes formed on the board need to be assured.
However, the required accuracy cannot be secured when mounting the above-described micro components at a narrow pitch just by improving the accuracy of the electrode position and the component mounting position. For example, a component held with a suction nozzle may interfere with an adjacent mounted component during placement if the component is even slightly off center, obstructing the placement operation. Alternatively, a solder bridge may be formed between solder portions printed on adjacent electrodes before placing components. This may cause short-circuiting between electrodes if reflow is applied to the solder bridge. Accordingly, conventional component mounting methods tend to generate defects when used to mount micro components at very narrow pitches.
The present invention solves the above disadvantages and aims to offer a component mounting method which reduces defects even when mounting of micro components at a narrow pitch.
The component mounting method of the present invention for mounting components and soldering them onto a board comprises the next steps:
(a) printing solder so as to shift and create a predetermined offset from the center of at least one of the electrodes formed on the board at positions for fixing components when bonding component terminals;
(b) placing components after solder printing in such a way that the placement position is shifted by the above offset with respect to the electrode center position;
(c) moving the components toward the electrode center after placing the components by heating the board to melt the solder; and
(d) securing the terminals onto the electrodes at fixing positions after moving the components by solidifying the solder.
The above offset value is normally determined by taking into account the self-aligning effect of melted solder while the electrodes and terminals are being soldered, and is set to an allowable spacing between the terminal position and electrode center when placing the components in the above step (b).
The movement in the above step (c) occurs as a result of the self-alignment effect.
This method allows less stringent spacing conditions to be applied for component placement and prevents the occurrence of defects during printing and mounting by shifting the position by the predetermined offset when printing solder onto the electrode or placing the component on the board.